even with the hassle of developing both iOS and Android, it's got to be less than handling all the browser edge cases for "HTML5."
As someone who deals with Android day in, day out, I really doubt that.
With HTML5 you've got maybe 4 or 5 targets to worry about, targets that have different problems but a limited number all the same.
x (desktop + tablet + smartphone). The same device issues you raise can occur with HTML5, sometimes aggravated by the lack of definitive differentiators/inflection points between devices. How do you detect whether you're on an iPad or an iPhone 6 Plus? CSS media queries still only rely on user-determined heuristics to run different bits of layout/presentation.
Yes, Android device compatibility and OS support variability is a huge concern. I've never done more than tinker with Android, so I can't speak to it, but the issues seem comparable with HTML5, albeit with better (more concrete) APIs. I'd give Android the slight edge here.